I took took I-40 from Flagstaff to Memphis, then down to Florida, once. that was a pretty mellow route, lots of truckers, more English speaking people. people are more friendly on the bible belt. I didn't hitch it though, I drove, but I got my kicks on route 66. plus I believe I-40 cuts across north of LA, so it would make a more smooth transition to the west coast, make the highway 101 more accessible.
I-10 seems somewhat appealing with New Orleans and Houston being on the way, but keep in mind that I-10 is the most traveled cross country Interstate. More Hitchers, more people saying "no speak english", less halfies in the ash trays at truck stops, less charitable people. I-40 has less hitchers less people saying "no speak english", more halfies in the ash trays at truck stops, more charitable people.